Two coherent sources 'P' and 'Q' produce interference at point 'A' on the screen, where there is a dark band which is formed between 4^th and 5^th bright band. Wavelength of light used is 6000 $$\mathop A\limits^o $$. The path difference PA and QA is

In diffraction experiment, from a single slit, the angular width of central maximum does NOT depend upon

In biprism experiment, 21 fringes are observed in a given region using light of wavelength 4800 $$\mathop A\limits^o $$. If light of wavelength 5600 $$\mathop A\limits^o $$ is used, the number of fringes in the same region will be

A double slit experiment is immersed in water of refractive index 1.33. The slit separationis 1 $$\mathrm{mm}$$ and the distance between slit and screen is $$1.33 \mathrm{~m}$$. The slits are illuminated by a light of wavelength $$6300\,\mathop A\limits^o $$. The fringewidth is